Technical Field
The present invention relates to an imaging unit capable of calculating a distance to a subject by imaging a three-dimensional image, a vehicle control unit using the imaging unit, and a heat transfer method for the imaging unit.
Description of Related Art
A so-called stereo camera is known as an imaging unit capable of calculating a distance to a target object, as eyes of a person. The stereo camera includes two monocular cameras. For example, the stereo camera is inter-connected with a vehicle control unit that controls a vehicle and configured to calculate a distance to a subject in front of the vehicle. As a result, the stereo camera can control operation of the vehicle depending on the calculated distance.
The two molecular cameras of the stereo camera are disposed on the same plane and fixed such that both optical axes of the cameras are parallel to each other. The stereo camera detects a parallax quantity of the subject by simultaneously imaging the same subject by the two molecular cameras and can calculate a distance to the subject based on the parallax quantity.
There is a plurality of important factors to calculate a distance by use of the stereo camera. It is important that a standard length which corresponds to a distance between the optical axes of the two monocular cameras is set to a predetermined value, and focal lengths of the two monocular cameras are configured to match with each other. Furthermore, it is also important that the optical axes of the two monocular cameras are maintained parallel. If one monocular camera is directed to a different direction from the other, the optical axes are not maintained parallel to each other. In such a state, the parallax quantity cannot be exactly detected. If the parallax quantity cannot be exactly detected, the distance to the subject cannot be exactly calculated, accordingly.
Therefore, it is important that the stereo camera has the same focal length so as to fit characteristics of lenses used for the two monocular cameras and the standard length continues to be maintained to have a designed value, so that the stereo camera calculates an exact distance. Moreover, it is important that parallelism of the optical axes of the two monocular cameras is set in a correct state at the time of assembling them and maintained in that state thereafter.
However, the important factors as described above are often changed depending on a sequential change in situation in installation environment of the stereo camera. That is to say, by the sequential change, a fixed portion of each monocular camera is deformed to become a state where directions (positions) of the monocular cameras differ from each other. Therefore, the parallelism of the optical axes is not maintained, or performance of each monocular camera is reduced by a change in temperature environment.
Therefore, a method of mounting a vehicle-mounted camera to hold a position of two monocular cameras is known (for example, see Japanese Patent No. 3877475). In the method, the two monocular cameras are fixed to both ends of one stay, and a center of the stay is fixed to a vehicle and so on. With this configuration, even if the stay is deformed by the influence of outside air temperature, the position of the two monocular cameras is held in a correct state.
As shown in the vehicle-mounted camera disclosed in Japanese Patent No. 3877475, it is needed to fix the vehicle-mounted cameras, that is, the monocular cameras to direct in front of the vehicle to measure a distance to a target object. The monocular cameras easily receive direct sunlight and are fixed to a position where a temperature easily becomes high. Each of the monocular cameras has heat-generating components in Large-Scale Integration (LSI) for processing an image. Therefore, temperature rise of the cameras occurs due to the heat from the heat-generating components. There is a possibility that the stay to fix the cameras is deformed by the temperature rise. Here, if the transfer of the heat from the heat-generating components of heat sources is not even over the entirety of the stay, there is a possibility that a fixed state of the stay and the cameras is deformed by thermal expansion due to the uneven heat distribution.
In particular, in the stay made of a metal as shown in the vehicle-mounted camera disclosed in Japanese Patent No. 3877475, if the heat distribution is uneven, the thermal expansion becomes uneven, and hence the stay is easily deformed. Because the vehicle-mounted camera is a stereo camera including the two monocular cameras, if the stay is unevenly deformed by the uneven thermal expansion, there is a possibility that the fixed state of only one of the monocular cameras is changed. As a result, the parallelism of the optical axes of the monocular cameras is not exactly maintained, or only one of the monocular cameras is heated and the characteristics of the monocular cameras decline. Thereby, the accuracy of the calculation of the distance is reduced.